This invention relates to an end surface seal which is used in the tread guide rollers, and the like of construction machinery such as bulldozers. More specifically, the present invention provides a sealing device which has a remarkably improved sealing action against leakage of lubricant and penetration of outside foreign matters, such as sand, mud, etc., during rotation of the guide roller and the like.
As an end surface seal for guide rollers of the above-described type, it is possible to employ an ordinary mechanical seal having a coil spring. Exemplary of improved seals such as this is the seal illustrated in FIG. 1 and FIG. 3 which has been used conventionally.
Referring first to the seal system shown in FIG. 1, a cylindrical floating seat 2 has a pair of end seal surfaces 3 which encompass shaft 1 and are placed in sliding contact with each other. An outer circumferential surface 4 of this floating seat 2 has a headed conical shape with the diameter thereof decreasing from the position adjacent to the end seal surface 3 axially away therefrom. An inner circumferential surface 6 of a housing 5 also has a frusto-conical shape similar to that of the outer circumferential surface 4 of the floating seat 2. The outer circumferential surface 4 of the floating seat 2 and the inner circumferential surface 6 of the casing 5 clamp an O-ring 7, made of a rubbery elastic material therebetween in a compressed and twisted state in such a manner as to prevent leakage of a shaft lubricant and invasion of sand and mud from the outside. This is achieved by means of the pressed and sliding contact between the end seal surfaces 3 as well as the pressed contact between the outer and inner diameter sections of the O-ring 7.
The system of FIG. 1, however, is not free from inherent drawbacks, such as are mentioned below:
(A) Since the O-ring moves back and forth in its twisted state at the portion contacting the floating seat and housing, there takes place rapid wearing of the contact portion and accumulation of sand and mud.
(B) The contact portion of both the floating seat and housing with the O-ring has a conical shape; hence, it is not easy to maintain an adequate machining accuracy in size and shape.
(C) A load is generated by the elasticity of the O-ring so that it is necessary to maintain the hardness of the rubber at less than 70.degree. in conjunction with the tolerance in the fitting size.
(D) The shape of the floating seat is complicated, which increases the cost of production.
(E) Sealing is achieved by a load which is applied to the seal surface 3 by means of a deflection quantity of the O-ring. For this reason, it is an essential requirement that the load due to deflection reaches a specified level and, at the same time, the amount of the load should not be substantially non-uniform. In systems of the type shown in FIG. 1, the deflection-load characteristics are shown in the diagram of FIG. 2 at a load quantity required for achieving sealing, the change in the load quantity .DELTA. P.sub.1 relative to a change in the deflection quantity .DELTA. L.sub.1 increases. Since the change in the deflection quantity is caused by tolerance in the fitting dimension, there is a strict limitation on the tolerance in the fitting dimension to maintain it small in order to minimize the quantity of change in the load.
Referring now to the system shown in FIG. 3, the flange section encompasses a shaft 11 and has an end seal surface 13. A floating seat 12 comprises a cylinder which extends away from the flange section to an end seal surface 13. Thus, a back surface 14 of the flange section and an outer circumferential surface 15 of the cylinder section form an open section therebetween, and an annular surface 17 on a casing 16 opposes this open section to define a concavity between the open section, the annular surface 17 and the inner circumferential surface 18 of the cylinder. An annular packing 19, made of a rubber-like elastic material, is interposed into the resultant concavity in a compressed state in such a manner as to prevent leakage of a lubricant and invasion of sand and mud from the outside by means of pressed sliding contact of the seal surfaces 13 as well as pressed contact between the annular packing 19, the floating seat 12 and the housing 16.
As shown in FIG. 3, in the above-mentioned system, a load is generated by an angle of inclination of the annular packing 19 and by the hardness of the rubber. Hence, it is necessary either to lower the hardness of the rubber or to accurately maintain the sectional shape of the packing. Stated otherwise, it is required to make the ratio B/A large between the thickness A of the packing in the axial direction and the size B thereof in the direction of radius. (In this instance, it is necessary to make the ratio B/A more than 1.5.)
The deflection-load characteristics of the system of FIG. 3 is shown in FIG. 4. In a manner similar to the system shown in FIG. 1, a change in the load .DELTA. P.sub.2 due to a change in a deflection quantity .DELTA. L.sub.2 increases at a point where there is obtained a load which fully assures sealing. It is therefore imperative to minimize the tolerance in a fitting dimension as much as possible in order to maintain the non-uniformity of the load within a permissibly small range.